Wildlife and roads are a bad combination. But what is it about roads that harms animals the most? Is it the habitat fragmentation, the pollution, the car collisions, the noise?

While all these factors play a role, scientists haven’t been sure how important each one is. Some studies suggest that noise is particularly disruptive: For example, one team reported that songbirds were sparser near loud gas compressor stations. Other researchers have found that birds whose calls are drowned out by traffic sounds tend to stay away from roads.

To nail down the role of noise, the authors of a new study created a “phantom road” in the foothills of Idaho, where many migrating birds stop. They set up 30 speakers spread over half a kilometer along a ridge, then played recordings of traffic sounds for four days at a time. During other four-day periods, the speakers were silent.

The team also observed birds in the area from 59 species, including robins, sparrows, finches, chickadees, and thrushes. When the traffic noise was on, the number of nearby birds dropped by 28 percent, the researchers report in Proceedings of the Royal Society B. Cedar waxwings and yellow warblers were particularly sensitive to the ruckus.

“We substantially depleted the population of migratory birds and caused entire species to almost completely avoid an otherwise high-quality stopover site,” the team writes. That’s worrisome because some species may be losing out on habitat spots “simply because they are too loud.” — Roberta Kwok | 7 November 2013

Source: McClure, C.J.W. et al. 2013. An experimental investigation into the effects of traffic noise on distributions of birds: avoiding the phantom road. Proceedings of the Royal Society B doi: 10.1098/rspb.2013.2290.